One of the main purposes of this research effort is to perform electron and light microscopic studies, utilizing cytochemistry, morphometry, and radioautography, and analyze the mechanism for hyperplastic activity of the gastric mucosa as a result of small bowel resection. In addition to these efforts, scanning and transmission electron microscopic studies and light microscopic studies will be made in order to evaluate the destructive effects of bile and aspirin solutions on the gastric mucosa. Studies will be conducted on the gastric glands to determine the presence of cellular contacts and gap junctions which represent electrical couples, sites of ion transfer, and low resistance pathways between cell membranes. Additional studies will be performed to determine the localization sites of carbonic anhydrase activity in tissue slices, isolated cells, and subcellular fractions of cells of the gastric glands following stimulation and inhibition of gastric secretion.